<?php
session_start();
header('Content-type:image/gif');
$image_w=100;
$image_h=25;
$number=range(0,9);
$character=range("Z","A");
$result=array_merge($number,$character);
$string="";
$len=count($result);
for ($i=0;$i<4;$i++){
    $new_number[$i]=$result[rand(0,$len-1)];
    $string=$string.$new_number[$i];
}
$_SESSION['string']=strtolower($string);
$check_image=imagecreatetruecolor($image_w,$image_h);
$white=imagecolorallocate($check_image,255,255,255);
$black=imagecolorallocate($check_image,0,0,0);
imagefill($check_image,0,0,$white);
for ($i=0;$i<100;$i++){
    imagesetpixel($check_image,rand(0,$image_w),rand(0,$image_h),$black);
}
for($i=0;$i<count($new_number);$i++){
    $x=mt_rand(1,8)+$image_w*$i/4;
    $y=mt_rand(1,$image_h/4);
    $color=imagecolorallocate($check_image,mt_rand(0,200),mt_rand(0,200),mt_rand(0,200));
    imagestring($check_image,5,$x,$y,$new_number[$i],$color);

}

imagepng($check_image);
imagedestroy($check_image);
?>
